The present description relates generally to methods of and apparatuses for evaluating the performance of a control system. More specifically, the present description relates to automated methods of and apparatuses for evaluating the performance of a control system which utilize a series of tests, such as standardized tests.
It is known to use feedback control loops in modern heating, ventilating, and air-conditioning (HVAC) control systems and proportional plus integral action is the most commonly employed control law. Despite the prevalence of this standard and well-understood control strategy, building performance is frequently hampered by poorly performing feedback control loops. System controllers utilizing feedback control loops are often badly tuned, which may lead to sluggish or oscillating system responses. Other times, the plant (i.e., the device or other part of the system to be controlled) deteriorates or malfunctions to such a degree that it can no longer be controlled. In the latter case, bad tuning might be suspected and extensive time may be expended trying to re-tune the loop before discovering that the system cannot be controlled with proportional plus integral action.
Commissioning typically relates to testing and verifying the performance of a feedback control loop. Performing proper commissioning could eliminate many of the problems with feedback control loops in control systems. Commissioning is normally performed after control systems have been installed and before they are brought into full operation while there is still an opportunity to perform tests to verify acceptable performance. This opportunity is often not taken advantage of due to time constraints, limited availability of skilled personnel, a large number of control loops and large amounts of data, and a lack of standardized and repeatable test procedures. The result of inadequate commissioning is that installation, configuration, and tuning problems are not identified and then persist, sometimes throughout the life of the buildings.
Many commissioning-type problems may not be detected during the life of a building due to the effect of compensatory action between interacting control systems. For example, a heating coil further downstream may mask a leaking cooling valve in a duct system. Or a faster reacting loop may be masking the oscillations in a slower loop. Often a problem is only deemed to exist when occupants are dissatisfied or energy use is significantly affected and in many cases only the severest problems will be noticed. Further, once a problem is detected during the normal operation of a building, the same kind of issues that were faced during commissioning arise once again. For example, there are time constraints, due to cost, for fixing the problem; a lack of skilled personnel; large numbers of control loops generating overwhelming amounts of data, and a lack of standardized tests.
In view of the foregoing, it would be desirable to provide a method of and apparatus for evaluating the performance of a control system, such as a control loop in an HVAC system, that makes the adoption of more rigorous commissioning and troubleshooting more practicable and less time consuming by utilizing automated standardized test procedures which may be carried out in parallel on multiple feedback control loops.
Additionally, many system controllers operate as regulators with fixed setpoints, and for some types of control systems, the artificial introduction of a setpoint change for purposes of performance assessment may be impractical. For other systems, little or no information about certain control system parameters may be available. Thus, it would further be desirable to provide a method of and apparatus for evaluating the performance of a control system which provides not only invasive testing techniques, but also non-invasive testing techniques which do not disturb normal operation of the control system. It would also be desirable to provide a method of and apparatus for evaluating the performance of a control system which requires little or no prior information about a particular feedback control loop.